[time-nuts] Homebrew WWVB TX simulator?

Magnus Danielson magnus at rubidium.dyndns.org
Tue Sep 14 22:12:42 UTC 2010


On 09/14/2010 11:49 PM, Hal Murray wrote:
>
>> Maybe a PIC to do the modulations trains and a serial interface to set  it
>> up. In all about 3-4 chips. Should not be too hard.
>
> Why do you need more than one chip?
>
> Why can't the PIC generate the 60 KHz signal by bit banging a couple of pins?
>   I'm thinking of a 2 or 3 bit D/A with 2 or 3 more pins for the low power
> portion of the signal.
>
> 1 bit might be enough with a good external filter.

It may not be the simplest solution to be the minimal chip-count 
solution. By all means, knock yourself out. My intention was for a 
simple solution where each part would be simple and clear. If you 
bit-bang the hell out of a PIC it will be more tedious but you can get 
the result.

I'm proud owner of two TADD-2 PIC-dividers... so I am not against the idea.

You can always write software that beeps 12 kHz out of a 48 kHz 
soundboard (4-sample carrier wave) and then use a transistor as a 
distortion stage (2N3904?) filter away junk (optional) and use the 5th 
overtone distortion for carrier. Maybe a diode (1N914 or 1N4148) may 
work just as well.

The tone-lengths is 200 ms, 500 ms and 800 ms so looping the sample 
stretches should be trivial, as you have 12 waveforms per ms and need to 
modulate 200 ms and 300 ms stretches of the two amplitude-levels to form 
the second pulses.

I am tempted to try it out with the laptop or builtin audio of a 
crapiola PC. Should not be too hard. Far simpler than bit-banging a PIC.

Cheers,
Magnus




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